The molecular mechanisms that regulate stem cell self renewal and differentiation are crucial for embryonic development and for long term tissue maintenance and repair. Understanding these mechanisms will be key for harnessing the potential of adult stem cells for regenerative medicine. We propose to identify molecular mechanisms that regulate adult stem cell self- renewal, maintenance and asymmetric division to maintain tissue homeostasis throughout life. Using the Drosophila male germ line as a model system, we discovered that support cells provide a crucial microenvironment that regulates both stem cell self renewal and differentiation, and that stem cells orient toward this niche to set up a stereotyped mitotic spindle, ensuring the normally asymmetric outcome of stem cell divisions. We now propose to utilize the powerful system and tools we have established to identify the molecular circuitry that regulates stem cell behavior in response to cues from the niche. We will elucidate the cellular mechanisms that orient stem cells to the niche to specify asymmetric division and investigate how insulin receptor signaling components affect stem behavior. To elucidate the transcriptional regulatory network that specifies stem cell fate downstream of niche signals, we will investigate the regulation and mode of action of /o/a BTB domain-Zn finger protein(s), identify and investigate the function of targets of activated STAT in stem cells, and place genes that regulate stem cell behavior in the context of known stem cell regulatory pathways. To investigate the potentially conserved role of epigenetic silencing in regulating stem cell behavior, we will test roles of Polycomb group transcriptional repression machinery, including PRC2 components and BmM homologs, as well as chromatin remodeling components, in stem or progenitor cell self-renewal, division or differentiation.